There are four DNA bases, Adenine (A), Cytosine (C), Guanine (G) and Thymine (T).
On each strand of DNA, the DNA bases are connected by phosphodiester bonds, to form a long chain.
These long DNA strands are paired and mirror each other to form the DNA double helix. The DNA bases pair to their mirrored base in two ways: A-T or C-G.
These paired bases between the DNA strands bond by hydrogen bonds. There are two hydrogen bonds between A-T and three between C-G.